1. Field of the Invention
This invention relates to a resistance change memory device with a memory cell for storing a resistance state of a variable resistance element in a non-volatile manner, specifically to a technique for measuring against defective memory cells.
2. Description of the Related Art
A resistance change memory device (resistance RAM: ReRAM) has been proposed to store a resistance value as data, which is reversibly exchanged by applying voltage, current or heat, and it is noticed for succeeding to the conventional flash memory. This ReRAM is suitable for shrinking the cell size, and for constituting a cross-point cell array. In addition, it is easy to stack cell arrays.
Especially, a unipolar type of ReRAM is settable in a high resistance state or a low resistance state by controlling the applied voltage value and applying time (for example, Y. Hosoi et al, “High Speed Unipolar Switching Resistance RAM(RRAM) Technology” IEEE International Electron Devices Meeting 2006 Technical Digest p. 793-796).
However, there is such a probability in ReRAM that as the high integration progresses, the number of defective cells increases. It is usually used a diode as an access element of a ReRAM's memory cell, and cell selection is performed by use of the difference between the forward-bias state and the reverse-bias state. In this case, if cell leak is generated at a cross point cell, there is a probability that the cell bias may be reversed in other cells coupled to a word line or a bit line coupled to the defective cross point cell. Therefore, the influence of the defective cell is large. Specifically, this becomes a large problem in case of achieving a large capacitive ReRAM with a three dimensional (3-D) cell array structure.